Electric water heater not heating: from the ELCB to the element (which you do not open yourself)

• Switch off the MCB and unplug the appliance before checking anything.
• Make sure your hands and the floor are dry.
• Close the main water valve before opening any water connection.
• Keep water away from sockets and plugs.
• Let the appliance cool down before touching anything inside it.
• Keep your hands and face away from hot steam.

Water heaters are installed in bathrooms, where everything gets wet. Do the ELCB test and every other check with dry hands, standing on a dry floor.

Homes usually have one of two types of electric water heater. A storage (tank) type holds water in a tank and heats it slowly with a fairly low-power element; the Modena Unica manual lists a rated heating power of 250W/350W. Because the power is low, the tank takes time to heat cold water, and the hot water can run out when several people shower one after another. An instant (tankless) type has no tank and heats the water as it flows, at a much higher power; the Modena Onyx manual lists 2400W for one of its models.

The type decides what to check. On a storage type, the question is whether the heater is getting power and whether it has been on long enough. On an instant type, the question is whether there is enough power and whether the water flow is strong enough to switch the heater on. The Onyx manual says the water comes out cold if the flow is less than 1.5 liter per minute.

In Indonesian homes on a low-VA PLN connection, an instant water heater often trips the MCB when it runs at the same time as other appliances.

Many electric water heaters have an ELCB, an earth leakage (ground fault) safety device, usually built into the plug with a test button and a reset button. If the ELCB cuts the power, the water heater will not heat even though it is plugged in. Modena's storage water heater manual explains how to check it:

1. Plug the heater into the socket.
2. Press the test button. The indicator light on the plug should go out and the reset button should pop up.
3. Press the reset button. The indicator light comes back on, which shows that the leakage protection is working properly.

The same manual explains two abnormal results. If the reset button cannot be pressed in during use, the ELCB is faulty. If you press the reset button and it pops up again, the circuit is leaking or the power is off. Either way, do not force the button or wedge it down; stop using the heater.

For the instant type, the Modena Onyx manual says to check the built-in ELCB once a month. It names an ELCB indicator light that is off, or code E5 on the display, as signs of a power supply problem, a circuit board (PCB) problem or current leakage.

1. Socket and plug. Modena's storage water heater manual says the socket must be properly grounded and rated at no less than 16A, and the socket and plug must be kept dry. If the socket or plug feels too hot, is loose or is scorched, stop here and call an electrician.
2. No timer. The same manual forbids connecting the heater through an external switch such as a timer, because it can reset the thermal protection by accident.
3. Knob and lights. On a storage type, the green power LED and the red heating LED light up when there is power, and the red LED goes out when the water reaches the set temperature. Turn the temperature knob up and give it time, because the heater has to run for a while to reach the temperature you set.
4. Water in. The heater must not be switched on until the tank is completely full of water, and according to the manual the inlet valve must stay open during normal use. Make sure the cold-water valve to the heater is not closed.
5. Flow on an instant type. Open the faucet more. The Onyx manual names dirt blocking the rotor in the flow regulator as one cause of cold water; clean the shower head and any strainer you can remove without opening the heater's housing.
6. Codes on the display. On the Onyx EI 0340 RDBG, code E3 is linked to a thermal sensor that has cut out or to a damaged element. Codes like these are not something to fix at home.

A storage water heater has a thermal switch that cuts power to the element if the water gets too hot or there is no water in the tank. The Modena manual explains the symptom: if the heater is plugged in but the water does not get hot and the indicator light is off, the thermal switch has tripped. Resetting it means removing the front cover plate, and the same manual states firmly that non-professionals must not take apart or reach into the thermal switch to reset it.

Water that contains lime or silt coats the element with scale, so heating slows down. The Modena manual says the element should be descaled every year by the service center. It also says the magnesium anode must be replaced within two years at most if the water quality is good, or within one year if it is poor. In areas that use hard well water, this schedule matters even more.

There is one maintenance task the manual gives to the owner: open the safety valve regularly, at least every six months, to flush out lime deposits. The water that comes out of this valve is hot, so do it after the heater is switched off and the water has cooled, and never block the safety valve's outlet.

Contact the authorized service center for your water heater's brand, or a qualified technician, if:

• the ELCB reset button keeps popping up or cannot be pressed;
• the heater is plugged in but the indicator light is off and the water is not hot (the thermal switch needs checking);
• the heating light is on but the water stays cold, or the water gets too hot (the Modena manual names a failed temperature control or heating element as the cause);
• the display shows an error code, or a safety light blinks;
• too much water drips from the safety valve, a connection or gasket leaks, or the socket feels hot;
• it is time to descale the element or replace the magnesium anode.

Resetting the thermal switch behind the cover, opening the thermostat, replacing the heating element and replacing the power cord are jobs for a technician. The Modena manual says only a technician or a qualified person may replace the cord. The socket, the grounding and a dedicated MCB for the water heater should be installed by an electrician.